Landing pad technology doubled up as a local interconnect and borderless contact for deep sub-half micrometer IC application

ABSTRACT

The present invention is directed to a technology that simplifies the process of fabricating multilayer interconnects and reduces capacitance in integrated circuits employing multilayer interconnects. The novel landing pad technology of the present invention simplifies the current process steps involved in the formation of multilayer interconnects. The same contact/via etch, the same PVD TiN deposition, etc., can be modularized and repeated to build up multilayer metalization. The process of the present invention for forming multilayer interconnects involves the formation of Ti/TiN stack interconnect structures that can be used as local interconnects and contact landing pads on the same level. The contact landing pads facilitate the use of a borderless contact approach which enables a reduction in the size of the source-drain area. As the source-drain area is reduced, junction capacitance decreases, and packing density can be increased. Source-drain real estate can be also be minimized by using the Ti/TiN stack interconnect structures as contact landing pads in the implementation of raised source-drain technology. The Ti/TiN stack interconnect structures can also be used as short local interconnects in SRAM devices.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 08/466,649 filed Jun. 6,1995, pending.

This application is related to the application Ser. No. 08/470,302,filed on even date herewith now abandoned. That application concerns theformation of a Ti/TiN landing pad at the base of contact and viaopenings in a dielectric to improve the throughput of the process forfabricating multilayer interconnects. The present application isdirected to a technology which employs Ti/TiN stack interconnectstructures as local interconnects and contact landing pads to simplifythe process of fabricating multilayer interconnects, to allow fortighter lay-out rules for die-size reduction, as well as to reducecapacitance in integrated circuits.

TECHNICAL FIELD

The present invention relates generally to semiconductor processing,and, more particularly, to simplifying the process of fabricatingmultilayer interconnects, allowing for tighter lay-out rules fordie-size reduction, as well as reducing the RC time constant ofintegrated circuits (ICs) employing multilayer interconnects.

BACKGROUND ART

With increases in circuit speed and miniaturization of ICs, parasiticeffects become the bottleneck of IC performance. The RC time constantbecomes the dominate part in controlling the performance of IC circuits,especially microprocessors. There are two different paths to controllingthe contribution of parasitic effects.

The first path is to control the passive parasitic effects ininterconnect systems which form connections to the source, gate, anddrain electrodes. In such interconnect systems, metal connections aremade by multilayer interconnects supported over the substrate by aninterlayer dielectric. To control passive parasitic effects ininterconnect systems, technologists have proposed to use low dielectricconstant materials such as SiOF, BN, polyimides, Teflon™, BCB(benzocyclobutene), and other spin-on materials as the dielectric, sothat the conductor-to-conductor coupling is minimized. Others haveproposed to use low-resistance interconnect systems based on lowresistance conductors such as copper, gold, etc. Still others haveproposed to use "pseudo-low dielectric constant technology", i.e.,exchange complexity for relaxed design rules such that more metalinterconnect layers are used and each layer can use less aggressivedesign rules; see patent application Ser. No. 08/330,767, filed on Oct.28, 1994, by K. W. Cheung entitled "Pseudo-low Dielectric ConstantTechnology", now U.S. Pat. No. 5,471,093, issued Nov. 28, 1995.

The second option for controlling the contribution of parasitic effectsin integrated circuits is to control the active capacitance. Sometechnologists have proposed to lower the active capacitance, i.e.,minimize the overlap capacitance of the transistor by reducing theMiller capacitance. The LDD (lightly doped drain) approach is oneproposed technology that can minimize Miller capacitance. Others haveproposed a "Raised Source-Drain" technology for minimizing thesource-drain area and hence reducing the capacitance.

In addition to controlling parasitic effects, low-resistanceinterconnect systems are useful in other applications. In particular,there is also a need for low resistance local interconnects for someapplications in SRAM (static random access memory) technology. With theadvance of local interconnect (LI) technology, one can optimize the cellsize of the SRAM core cell and provide highly competitive SRAMtechnologies. Accordingly, some technologists have proposed "amorphousSi LI" technology comprising Si/Ti interconnect structures. Others haveproposed "Stable LI technology" comprising Si/Ti/TiN/Ti interconnectstructures, see, e.g., patent application Ser. No. 08/309,692, filed onSep. 21, 1994, by S. Ramaswami et al entitled "A Stable LocalInterconnect/Active Area Silicide Structure for VLSI Applications", nowU.S. Pat. No. 5,451,545, issued Sep. 19, 1995. Still others haveproposed TiN as the LI structure.

All the proposed interconnect systems discussed above can provide somerelief to technology, requirements in one form or another; however, noneprovide a comprehensive solution. Accordingly, there remains a need forsuch comprehensive solution.

DISCLOSURE OF INVENTION

In accordance with the invention, a process is provided for formingmultilayer interconnects which involves the formation of Ti/TiN stackinterconnect structures that can be used as local interconnects andcontact landing pads on the same level. The local interconnects andcontact landing pads directly contact conductive regions of asemiconductor integrated circuit. Contact may be formed withpreviously-doped regions in the semiconductor substrate, polysilicon, orother metal layers.

The process for forming multilayer interconnects for connectingconductive regions to conductive regions separated by insulating regionssupported on a semiconductor substrate comprises:

(a) forming a layer of Ti on the insulating regions and the conductiveregions;

(b) forming a first layer of TiN on the layer of Ti;

(c) patterning and etching the layer of Ti and the first layer of TiN toform at least one Ti/TiN stack interconnect structure selected from thegroup consisting of (1) a contact landing pad contacting one of theconductive regions, (2) a local interconnect contacting at least two ofthe conductive regions, forming electrical connection therebetween, and(3) a local interconnect contacting at least one of the conductiveregions and comprising at least one contact landing pad, formingelectrical connection therebetween;

(d) forming an interlayer dielectric over the semiconductor substrate;

(e) etching contact openings in the interlayer dielectric down to atleast one of the contact landing pads or one of the local interconnects,each of the contact openings having a bottom and sidewalls;

(f) depositing a second layer of TiN such that the second layer of TiNis formed on the bottom and the sidewalls of the contact openings;

(g) depositing a layer of metal thereby filling the contact openingswith the layer of metal;

(h) removing the second layer of TiN and layer of metal outside of thecontact openings thereby forming metal plugs in the contact openings;and

(i) forming a first layer of metal interconnects on the interlayerdielectric contacting the metal plugs.

Any number of additional levels comprising additional layers of metalinterconnects can be formed by repeating a portion of the steps outlinedabove. The steps required to form additional levels involve forming anadditional interlayer dielectric, etching additional contact/viaopenings, depositing an additional second layer of TiN, filling theadditional contact/via openings with an additional layer of metal,forming additional metal plugs, and forming an additional layer of metalinterconnects. With the novel landing pad technology of the presentinvention, the processing is truly modular, i.e., process steps will beidentical from one level of metalization to another.

In accordance with present invention, the contact landing pad mayoverlap the insulating regions surrounding the contact landing pad. Theoversized contact landing pad facilitates the use of a borderlesscontact approach which enables a reduction in the size of thesource-drain area and a reduction in contacted source-drain designrules.

The insulating regions may comprise oxide as in the case where theinsulating regions are field oxide regions.

A portion of the insulating regions may comprise an insulating layerthat is formed on the conductive regions and field oxide regionssurrounding the conductive regions. The insulating layer is patternedand etched to form a window above at least one of the conductive regionsprior to forming the layer of Ti.

As indicated above, the Ti/TiN stack interconnect structures of thepresent invention can be used as local interconnects and contact pads onthe same level.

The Ti/TiN stack interconnect structures of the present invention can beused as contact landing pads for source-drain electrodes.

The Ti/TiN stack interconnect structures of the present invention canalso be used as local interconnects to contact cross-coupled static SRAMcell pull-up and pull-down transistors effectively without increasingthe cell size. The standard prior art technology uses multiple levels ofinterconnect metalization. The standard prior art technology usuallyoccupies more real estate.

The present invention simultaneously provides the following:

1. a technology that can provide local interconnect requirements ofroughly about 5 ohms/sq sheet resistance;

2. a technology that can provide a raised source-drain application sothat the source-drain real estate area can be minimized;

3. a technology that can provide a borderless contact approach, wherebythe contact opening can fall off the source-drain area and yet providegood electric characteristics; the use of borderless contacts having theadded benefit of reducing source/drain parasitic capacitance;

4. a technology that is compatible with the "monolayer technology" foradvanced BEOL (back-end-of line) tungsten applications; see patentapplication Ser. No. 08/402,254, filed Mar. 10, 1995, by R. J. Huang,entitled "Low Cost Solution to High Aspect Ratio Contact/Via AdhesionLayer Application for Deep Sub-half Micrometer Back-end-of LineTechnology";

5. a technology that is compatible with existing tooling in the factorywherein new hardware is not required, translating to low-cost as well ashighly manufacturable technology; and

6. a technology, with the raised source-drain and borderless contactprovision, which can support much reduced source-drain real estate,hence, increasing the packing density.

Other objects, features, and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionand accompanying drawings, in which like reference designationsrepresent like features throughout the Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings referred to in this description should be understood as notbeing drawn to scale except if specifically noted. Moreover, thedrawings are intended to illustrate only one portion of an integratedcircuit fabricated in accordance with the present invention.

FIGS. 1a-1h are cross-sectional views depicting a process of theinvention and the resulting structure.

FIG. 2 is a cross-sectional view depicting the resulting structure ofthe present invention after multilayer metalization.

BEST MODES FOR CARRYING OUT THE INVENTION

Reference is now made in detail to a specific embodiment of the presentinvention, which illustrates the best mode presently contemplated by theinventors for practicing the invention. Alternative embodiments are alsobriefly described as applicable.

The present invention is directed to a landing pad technology thatenables the formation of local interconnects and borderless contactsthat make contact with conductive regions of a semiconductor integratedcircuit. Contact may be formed with previously-doped regions in thesemiconductor substrate, polysilicon, or other metal layers. Contactsmade to doped regions in the semiconductor substrate or to a titaniumsilicide layer on doped regions in the semiconductor substrate becomesource or drain contacts. Contacts made to a polysilicon layer or atitanium silicide layer (titanium polysilicide, in this case) on apolysilicon layer which is formed over a thin oxide gate layer becomegate electrodes. Contacts may also be made to polysilicon lines or atitanium silicide layer (titanium polysilicide, in this case) on apolysilicon line as well as to metal interconnect lines with theproposed landing pad technology of the present invention.

FIG. 1a is a cross-sectional view of a wafer comprising a semiconductorsubstrate 10, such as silicon, on which is formed a plurality ofconductive regions (i.e., doped regions) 12. Field oxide regions 14separate the doped regions 12 from each other. A polysilicon line 16 isshown formed on the surface of one of the field oxide regions 14, withoxide spacers 18 on the sides thereof. While one such polysilicon line16 is shown, it will be readily apparent to those skill in the art thatin fact a plurality of such polysilicon lines exist on field oxideregions 14 on the semiconductor substrate 10 of an integrated circuit.

A titanium silicide layer 20 is formed on the doped regions 12 in thesemiconductor substrate 10 while a titanium polysilicide (or polycide)layer 22 is formed on the surface of the polysilicon line 16. Theformation of the titanium silicide layer 20 and titanium polysilicidelayer 22 is completed by rapid thermal anneal. The excess non-reactedtitanium is selectively stripped off and a second anneal is providedthereafter.

An insulating layer, (i.e., an oxide layer) 24 comprising PECVD (plasmaenhanced chemical vapor deposited) SiO₂ which can be TEOS (tetra-ethylorthosilicate) based is formed as shown in FIG. 1b. The PECVD SiO₂ canalso be SiH₄ based or even HDP (high density plasma) based CVD (chemicalvapor deposited) SiO₂. The insulating layer 24 may also comprise siliconoxy-nitride or Si₃ N₄. The requirements for this insulating layer 24 aregood film uniformity and that the insulating layer serves as a goodmoisture barrier. Based on literature, the best barrier is Si₃ N₄,followed by HDP-based CVD SiO₂, and silicon-rich SiH₄ -based PECVD SiO₂,in that order. The thickness of the insulating layer 24 ranges from 500Å to 2000 Å; the preferred thickness being about 1000 Å. The insulatinglayer, or oxide layer 24 is patterned using a local interconnect andlanding pad window mask and etch. FIG. 1b illustrates the structure ofthe device after the removal of the mask. The window on the titaniumpolysilicide (or polycide) layer 22 on the surface of the polysiliconline 16 can be oversized.

In accordance with the invention, a Ti/TiN stack 26 comprising a layerof Ti 28 and a layer of TiN (first layer of TiN) 30 is formed asdepicted in FIG. 1c. The layer of Ti 28 is deposited before the firstlayer of TiN 30 in a cluster PVD (physical vapor deposition) tool. Thelayer of Ti 28 serves to reduce contact resistance, enhance TiN adhesionon the surface of the field oxide regions 14, and reduce the resistivityof the Ti/TiN stack 26 for local interconnect applications.

The process technology can use relaxed temperature settings foroptimization of resistivity. Typically, to form titanium silicide abovea junction, a rapid thermal anneal (RTA) is performed at about 600° C.to 650° C. With higher temperatures, more silicon at the junction isconsumed in forming thicker titanium silicide. The shallow junctionsemployed in current 0.35 μm and future 0.25 μm and 0.18 μm technologies,however, require minimum silicon consumption. Accordingly, a lowertemperature RTA is preferred. Reduction in RTA temperature producesthinner titanium silicide and less silicon consumption, but results inhigher contact resistance. The layer of Ti 28 used in the presentinvention reduces contact resistance enabling the use of relaxedtemperature settings that optimize resistivity. If the first layer ofTiN 30 is deposited after metal deposition, however, temperature optionsmay be limited due to "metal ring and worm" defects which are caused bythe mismatch in metalization processing temperatures.

The thickness of the layer of Ti 28 and the first layer of TiN 30 isoptimized based on device requirements. For a 400° C. set-pointprocessing of TiN, one should be able to achieve about 60 μΩ-cm bulkresistivity for the first layer of TiN 30. The optimized Ti process canalso give about 60 μΩ-cm bulk resistivity for the layer of Ti 28. Thus,the total thickness required for this Ti/TiN stack 26 to achieve 5 Ω/sqis about 1000 Å. The total recommended thickness is about 350 Å for thelayer of Ti 28 and about 800 Å for the first layer of TiN 30.

Next, the layer of Ti 28 and the first layer of TiN 30 are patternedusing a local interconnect and contact landing pad window mask and etch.A series of Ti/TiN stack interconnect structures 32 (shown in FIG. 1d)are produced from the etched layer of Ti 28 and the etched layer of TiN30. FIG. 1d illustrates the structure of the device after the removal ofthe mask. These Ti/TiN stack interconnect structures 32 serve as localinterconnect and contact landing pads. The local interconnect andcontact landing pads can be oversized to increase alignment tolerances.The borderless contact is an example where an oversized contact landingpad enables increased alignment tolerances.

The Ti/TiN stack interconnect structure 32 (left side of FIG. 1d)connecting the polysilicon line 16 with one of the doped regions 12demonstrates the use of the landing pad technology as a short localinterconnect as well as a contact landing pad/borderless contact. TheTi/TiN stack interconnect structure 32 contacting one of the dopedregions 12 (right side of FIG. 1d) illustrates the use of the landingpad technology as a contact landing pad/borderless contact. The Ti/TiNstack interconnect structure 32 over one of the field oxide regions 14(right side of FIG. 1d) demonstrates the use of the landing padtechnology as a contact landing pad for the rest area in theimplementation of raised source-drain technology (to be discussed morefully below). In a similar manner the Ti/TiN stack interconnectstructures 32 of the present invention can be used as short localinterconnects in SRAM devices, as contact landing pads/borderlesscontacts for source-drain electrodes and as contact landing pads in theimplementation of raised source-drain technology. In particular, theTi/TiN stack interconnect structures 32 of the present invention can beused as short local interconnects to contact cross-coupled static SRAMcell pull-up and pull-down transistors effectively without increasingthe cell size.

After masking and etching, the Ti/TiN stack interconnect structures 32are exposed to a rapid thermal anneal. The RTA step, which is performedafter the local interconnect and the contact landing pad patterning,will help ensure good adhesion of Ti to the oxide. Accordingly, the RTAimproves the adhesion of Ti/TiN stack interconnect structures 32 on thefield oxide regions 14. At the same time the RTA reduces the Ti reactionto oxide in the field area, preventing undesired residue clean-up inlater processing steps. The RTA, consistent with the current barriermetal deposition (BMD) annealing processes, is performed at 600° C. inan N₂ ambient for a period of 60 seconds.

This RTA step results in further reaction of the titanium silicide layer20 formed on the silicon, with the desired outcome of lowering thecontact resistance. The RTA allows the Ti deposited on the titaniumsilicide layer 20 to consume the native oxide, which is approximately 20Å thick and which is formed on the silicided and salicided areas.Accordingly, the Ti is transformed into titanium silicide to improvecontact resistance. If TiN is deposited on the titanium silicide layer20, the native oxide will not be consumed.

FIG. 1e shows an interlayer dielectric 34 which is deposited after theformation of the Ti/TiN stack interconnect structures 32. A contact maskand etch is employed to form contact openings 36 in the interlayerdielectric 34. The contact etch stops on the first layer of TiN 30 withminimum loss. FIG. 1e illustrates the structure of the device after theremoval of the mask. Use of the first layer of TiN 30 on the contactlevel as an etch stop serves to preserve the shallow junction in thedoped regions 12 beneath the patterned layer of Ti 28. The oversizedcontact landing pads ease alignment tolerances for the contact openings36. The present invention simplifies the production process as existingvia etch recipes can be employed. In such via etch recipes, the via etchstops on a TiN layer, or TiN anti-reflection coating, on the surface ofa layer of metal interconnects with minimum loss, see, e.g.,above-mentioned patent application Ser. No. 08/402,254.

Next, the surface of the wafer is sputter-cleaned. A second layer of TiN(TiN adhesion layer) 38 is then deposited, as shown in FIG. 1f. Theminimum thickness requirement for this TiN adhesion layer 38 is to haveat least 50 Å on the field area and with possibly a monolayer of TiNoriginating from the TiN adhesion layer 38, provides good contactresistance and junction protection.

Next, a first metal stack layer is deposited on the surface of thewafer. The first metal stack layer is patterned with a mask and etch toform a first layer of metal interconnects 42. The first metal stacklayer, and thus the first layer of metal interconnects 42, comprises abottom layer 44 comprising TiN or Ti, a central layer 46 comprisingtungsten and a top layer 48 comprising TiN. FIG. 1g depicts thestructure of the device after the mask has been removed.

To form an additional level comprising an additional layer of metalinterconnects 142, an additional interlayer dielectric 134 is depositedas shown in FIG. 1h. A contact mask and etch is employed to formadditional contact/via openings 136. (Since openings are etched in theadditional interlayer dielectric 134 down to a metal layer, the openingsare hereinafter referred to as contact/via openings 136 and the etch isreferred to as a contact/via etch.) The contact/via etch stops on thefirst layer of TiN 48 on top of the layer of first metal interconnects42 with minimum loss. As indicated above, to simplify the productionprocess, existing via etch recipes can be used for the contact/via etch.Furthermore, the same contact etch process employed above can be used asthe contact/via etch process used at this stage as well.

As before, the surface of the wafer is sputter-cleaned. Next, anadditional TiN adhesion layer 138 is deposited. The same TiN depositionas discussed above is employed at this stage of processing as well.Again, the minimum thickness requirement for this additional TiNadhesion layer 138 is to have at least 50 Å on the field area and atleast a monolayer of TiN deposited on the sidewalls of the contact/viaopenings 136.

The deposition of the additional TiN adhesion layer 138 is followed bythe blanket deposition of a tungsten layer (not shown). Additional metalplugs 140 are formed by CMP or plasma etchback. The same blankettungsten deposition and CMP or plasma etchback processes discussed aboveare employed at this stage of processing as well.

An additional metal stack layer is deposited on the surface of thewafer. The additional metal stack layer is patterned with a mask andetch to form an additional layer of metal interconnects 142. Theadditional metal stack layer and thus the additional layer of metalinterconnects 142, again comprises a bottom layer 144 comprising atleast a monolayer of TiN deposited on the sidewalls of the contactopenings 36, see above-mentioned patent application Ser. No. 08/402,254.

The technology employed in this present step is scalable to high aspectratio contact openings 36 (as well as via openings) and to feature sizesbelow 0.25 μm. The use of a Ti/TiN contact landing pad at the bottom ofthe contact opening 36 eases concern about both PVD Ti/TiN and PVD TiNstep coverage and can extend the lifetime of low cost PVD technology.Consequently, there is no need for CVD TiN at least for severalgenerations.

By easing concern about TiN step coverage, the approach of the presentinvention achieves the desired affect of using Ti/TiN as a barriermetal, but avoids the problem of volcano defects. Volcano defects arecaused by Ti exposure during tungsten deposition, due to incomplete TiNcoverage. If the TiN step coverage is not complete enough to cover thelayer of Ti 28 with TiN, WF₆ employed in tungsten deposition will reactwith the Ti and form titanium fluoride. This gaseous titanium fluoridewill prevent tungsten deposition, build up pressure, and possibly causeexplosions. With complete TiN coverage, concern about Ti exposure andthe formation of tungsten volcano defects is avoided.

There is no need for RTA at this step. Also, no wet pre-clean, which hasalready reached its limitations, is required before deposition of theTiN adhesive layer 38. Prior art wet pre-clean involves addingsurfactant which is limited by surface tension from cleaning the smallcontact openings which are smaller than 0.2 μm.

The deposition of the TiN adhesion layer 38 is followed by the blanketdeposition of a tungsten layer (not shown) which fills the contactopenings 36 with tungsten. Chemical-mechanical polishing (CMP) or plasmaetchback is employed to remove any overfill areas, i.e., tungsten andTiN outside of the contact openings 36. FIG. 1g depicts a plurality ofmetal plugs 40 formed by CMP or plasma etchback. In this case, the metalplugs 40 comprise tungsten; however, the metal plugs may comprise othermetals such as copper, gold, and aluminum. Accordingly, a layer ofcopper, gold, or aluminum must be blanket deposited in place of thetungsten layer.

The TiN adhesion layer 38 on the sidewalls of the contact openings 36serves to structurally support the adhesion of the metal plugs 40. Thelayer of Ti 28 and the first layer of TiN 30 which are now at the bottomof the contact openings 36, along TiN or Ti, a central layer 146comprising tungsten and a top layer 148 comprising TiN. The same metalstack layer deposition and patterning processes as discussed above areemployed at this stage of processing as well. FIG. 1h depicts thestructure of the device after the mask has been removed.

In accordance with present invention, any number of additional levelscan be formed by repeating the steps outlined above. FIG. 2 depicts thestructure of the device after multilayer metalization. The elementscomprising each additional level are similar and accordingly possesslike reference numerals preceded by a digit to specify the level (e.g.,134 for the first level, 234 for the second level, etc.).

With the novel landing pad technology of the present invention, the BEOLprocessing is truly modular, i.e., process steps will be identical fromone level of metalization to another. No special process steps arerequired. The process for forming an additional layer of metalinterconnects 142 can be repeated as many times as required to providethe additional multilayer metalization as shown in FIG. 2.

The novel landing pad technology of the present invention alsofacilitates the use of a borderless contact approach where the use ofoversized contact landing pads increase alignment tolerances. Theborderless contact approach enables a reduction in the size of thesource-drain area as the source-drain area must no longer be widened toaccount for possible misalignment. The design rule used for standardprior art contact schemes is such that the source-drain area for acontact is typically 3× feature size; 1× feature size for the contactitself and 1× feature size surrounding the contact for overlayrequirements. With the present invention, the source-drain area forcontact can be reduced to no more than 2× feature size. Greater than 30%reduction in junction capacitance can be achieved. Design andfabrication will no longer be limited by the source-drain area, thushelping to relax the requirements for the source-drain feature area.Also, there is then no need to employ trench isolation or advancedbird's beak reduction LOGOS technology. More important, if metal pitchbecomes packing density limited, the metal pitch can be matched to thesource-drain area. The oversized contact landing pad will providerelaxed design rules. Thus, high performance and high yield cansimultaneously be achieved.

If the source-drain is not pitch limited for packing density, one canentertain the "raised source-drain" concept. This concept, in itssimplest form, is to place the contact landing pad on top of the fieldoxide regions 14 (e.g., right side of FIG. 1d) and to electricallyconnect this contact landing pad to the active area of the source-drain(i.e., doped regions 12) using a local interconnect. Rather than formingthe contact openings 36 directly above the active area of thesource-drain, the contact openings can be positioned above to the fieldoxide regions 14. By forming the contact openings 36 over the fieldoxide regions 14, where a wide contact landing pad can be placed, theactive area of the source-drain need not be widened to account forpossible misalignment. This approach will reduce the active areacapacitance, thus, increasing circuit performance.

Another option of this invention is that the insulating layer, or oxidelayer, 24, which serves as a local interconnect and landing pad windowmask, is not formed. The step of depositing, patterning and etching theoxide layer 24 is thus eliminated. This approach will require etchingthe Ti/TiN stack 26 and stopping on titanium silicide and titaniumpolysilicide in regions where local interconnects and contact landingpads are not to be formed. Accordingly, the etch must stop on titaniumsilicide and titanium polysilicide (rather than stopping on the oxidelayer 24) which is possible with some field oxide loss. Reducing thethickness of the field oxide regions 14, however, may not be a goodtrade-off. The added 1000 Å to 2000 Å of oxide helps relieve the fieldoxide loss issues and maintain the field threshold voltage.

Advantages of the Invention

The present invention provides several advantages:

1. The present invention is designed for 0.35 μm and 0.25 μm technologyas well as the generation beyond, i.e., to technology designed forfeature sizes less than or equal to 0.18 μm.

2. The Ti/TiN stack interconnect structures 32 can be used as localinterconnects and contact pads on the same level to fully utilize thematerial.

3. Use of the TiN as an etch stop on the contact level can protect thejunction during contact etch, simplify the etch process, and providebetter alignment tolerances.

4. The present invention can ease concern regarding step coverage of PVDfilms employed in current 0.35 μm and future 0.25 μm and 0.18 μmtechnologies.

5. The present invention can extend the lifetime of the low cost PVDtechnology and push back the need for high cost CVD TiN and damasceneprocesses (by "damascene" is meant a process in which trenches orcontact/via openings are formed and then filled with metal using CVD orPVD or other techniques, followed by a polish to remove any overfilledareas).

6. The present invention will simplify the current process steps, i.e.,the same contact/via etch, the same PVD TiN deposition, etc., can bemodularized and repeated to build up multilayer metalization.

INDUSTRIAL APPLICABILITY

The process of the invention for forming multilayer interconnects isexpected to find use in the fabrication of silicon-based semiconductordevices.

The foregoing description of the preferred embodiment of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in this art. Itis possible that the invention may be practiced in other fabricationtechnologies in MOS or bipolar processes. Similarly, any process stepsdescribed might be interchangeable with other steps in order to achievethe same result. The embodiment was chosen and described in order tobest explain the principles of the invention and its practicalapplication, thereby enabling others skilled in the art to understandthe invention for various embodiments and with various modifications asare suited to the particular use contemplated. It is intended that thescope of the invention be defined by the claims appended hereto andtheir equivalents.

What is claimed is:
 1. A process for forming multilayer interconnectsfor connecting conductive regions to conductive regions separated byinsulating regions supported on a semiconductor substrate, said processcomprising:(a) forming a layer of Ti on said insulating regions and saidconductive regions; (b) forming a first layer of TiN on said layer ofTi; (c) patterning and etching said layer of Ti and said first layer ofTiN to form at least one Ti/TiN stack interconnect structure selectedfrom the group consisting of (1) a contact landing pad contacting one ofsaid conductive regions, (2) a local interconnect contacting at leasttwo of said conductive regions, forming electrical connectiontherebetween, and (3) a local interconnect contacting at least one ofsaid conducting regions and comprising at least one contact landing pad,forming electrical connection therebetween; (d) forming an interlayerdielectric over said semiconductor substrate; (e) etching contactopenings in said interlayer dielectric down to at least one of saidcontact landing pads or one of said local interconnects, each of saidcontact openings having a bottom and sidewalls; (f) depositing a secondlayer of TiN such that said second layer of TiN is formed on said bottomand said sidewalls of said contact openings; (g) depositing a layer ofmetal thereby filling said contact openings with said layer of metal;(h) removing said second layer of TiN and said layer of metal outside ofsaid contact openings thereby forming metal plugs in said contactopenings; and (i) forming a first layer of metal interconnects on saidinterlayer dielectric contacting said metal plugs.
 2. The process ofclaim 1 wherein said conductive regions are selected from the groupconsisting of doped regions in said semiconductor substrate,polysilicon, and metal.
 3. The process of claim 2 wherein at least oneof said conductive regions comprises doped regions in the semiconductorsubstrate, or polysilicon and a titanium silicide layer is formed onsaid doped regions or a titanium polysilicide layer is formed on saidpolysilicon.
 4. The process of claim 1 wherein said contact landing padoverlaps said insulating regions surrounding said contact landing pad.5. The process of claim 1 wherein said semiconductor substrate isexposed to sputter cleaning prior to the deposition of said second layerof TiN.
 6. The process of claim 1 wherein said layer of metal comprisesmetal selected from a group of metals consisting of tungsten, copper,gold, and aluminum.
 7. The process of claim 1 wherein forming said firstlayer of metal interconnects comprises:(a) forming a metal stack layeron said interlayer dielectric; and (b) patterning and etching said metalstack layer such that said first layer of metal interconnects contactssaid contact openings.
 8. The process of claim 7 wherein said metalstack layer comprises a bottom layer comprising TiN or Ti, a centrallayer comprising tungsten, and a top layer comprising a layer of TiN. 9.The process of claim 1 wherein field oxide regions surround saidconductive regions and at least a portion of said insulating regionscomprise an insulating layer that is formed on said conductive regionsand said field oxide regions, said insulating layer being patterned andetched to form a window above at least one of said conductive regionsprior to forming said layer of Ti.
 10. The process of claim 9 whereinsaid insulating layer is selected from a group of insulators consistingof plasma enhanced chemical vapor deposited SiO₂ which is tetra-ethylorthosilicate based, plasma enhanced chemical vapor deposited SiO₂ whichis SiH₄ based, high density plasma based chemical vapor deposited SiO₂,silicon oxy-nitride, and Si₃ N₄.
 11. The process of claim 1 wherein saidlayer of metal is blanket deposited and removing said first layer of TiNand said layer of metal outside said contact openings is achieved bychemical mechanical polish or plasma etchback.
 12. The process of claim1 wherein additional levels comprising additional layers of metalinterconnects are formed by a process comprising:(a) forming anadditional interlayer dielectric over said semiconductor substrate; (b)etching additional contact/via openings in said additional interlayerdielectric, each of said contact/via openings having a bottom andsidewalls; (c) depositing an additional first layer of TiN such thatsaid additional first layer of TiN is formed on said bottom and saidsidewalls of said additional contact/via openings; (d) depositing anadditional layer of metal thereby filling said additional contact/viaopenings with said additional layer of metal; (e) removing saidadditional first layer of TiN and said additional layer of metal outsideof said additional contact/via openings thereby forming additional metalplugs in said additional contact/via openings; and (f) forming anadditional layer of interconnects on said additional interlayerdielectric contacting said additional metal plugs, said additional metalplugs forming electrical connection between said additional layer ofmetal interconnects and a separate layer of metal interconnects formedbeneath said additional layer of metal interconnects.
 13. The process ofclaim 12 wherein forming said additional layers of metal interconnectscomprises:(a) forming an additional metal stack layer on said additionalinterlayer dielectric; and (b) patterning and etching said additionalmetal stack layer such that said additional layer of metal interconnectscontacts said additional contact/via openings.
 14. The process of claim13 wherein said additional metal stack layer comprises a bottom layercomprising TiN or Ti, a central layer comprising tungsten, and a toplayer comprising a layer of TiN.
 15. The process of claim 12 whereinsaid additional layer of metal is blanket deposited and removing saidadditional first layer of TiN and said additional layer of metal outsidesaid additional contact/via openings is achieved by chemical mechanicalpolish or plasma etchback.